Operation and discharge of sodium cells



July 12, 1960 G. o. HAYES OPERATION AND DISCHARGE OF SODIUM CELLS Filed Sept. 24, 1957 I I z 1, 1/ 1 1 FIG.

OPERATION DISCHARGE or SODIUM CELLS Glenn 0. Hayes, Greenwich, Conn., assignor to Ethyl Corporation, New York, N.Y., a corporation of Delaware Filed Sept. 24, 1957, Ser. No. 685,902

4 Claims. (Cl. 204- 68) This invention relates to the manufacture of alkali .-metals. More specifically, the invention relates to a new .technique in the preparation of alkali metals, especially sodium, by the electrolysis of fused salts, and to the discharge and delivery of the sodium to subsequent operations.

The alkali metals, especially sodium, have long been .made .by the electrolysis of certain fused salt compositions. 1 Generally sodium is made: by theelectrolysis of afused .bath consisting of sodium chloride and calcium chloride. This operation is carried out in cells ofthe Downs type, originally disclosed in'the Downs I patent, U'.-S. 1,501,756. The characteristic of the Downs cell operation was the employment of a bottom mounted anode of carbonaceous material, surrounded by-a cylindrical type cathode, forming an annular electrolysis zone .between these two members. The sodium-was deposited upon the cylindrical cathode, andbecause of its lighter density than the fused electrolyte bath, roseto the top of the cell chamber.

This rising sodium stream was received by an inyerted trough or collector, which in turn was connected to an upwardly rising riser pipe projecting from the 'top of the cell. This riser pipe provided for the flow of the, sodium above the top level of the electrolyte bath, into the exterior of the cell under the influence of the greater specific gravity of the fused bath than the molten alkali metal product.

" a In commerical operation, a large number of such cells are placed in each factory or shop. The sodium produced by the cells is, unfortunately, not as pure as necessary, but contains a certain amount of co-present calcium further purification treatment, for example such as is described in Gilbert patent, U.S. 1,943,307. The Gilbert patent describes a method of sedimentation and partial filtration of the sodium product from a cell, wherein a large proportion of the calcium impurity and other contaminants are further removed.

In order to efiect this transport and cumulation, a portable transfer vessel is connected to each sodium cell and isprovided to accumulate the product of such a cell for a' period of, say, 24 hours. At the termination of such a period, the transfer vessel is moved adjacent the sedimentation-filtration apparatus of the Gilbert device, and emptied, and later is returned for reattachment to the sodium cell. In additionto the transport vessel,

however, each cell was provided with an intermediate individual hold-up tank. This tank, or receiving drum.

was-usually a small drum permanently attached to the cell. The receiver drums were connected to the riser pipe of the cell, and sodium leaving the riser pipe passed through an opening directly into the receiver foraccumulationand then delivery to the transport ves- Zia 4930 Patented July 12, 1960 sel. Each receiver was provided with a stirring attachment for manual agitation so that further cooling and deposition of additional calcium from the crude sodium would not clog or foul up the discharge of the receiver drum to the transport vessel already mentioned.

This above described apparatus and method of operation has been not too satisfactory and has been quite expensive in operating labor demands. Because of the necessity of frequent agitation of the crude sodium in the intermediate storage vessels or receiver drums attached to each cell, manual attention at relatively frequent intervals was necessary. In addition it was necessary to rod out the channels or openings several times a day. The problem of eliminating this intermediate accumulation was heretofore thought insoluble. Automatic operation further, would have required quite expensive equipment to provide the agitation required and to clean out the intake to and discharge from the receiving drum. l

From the foregoing it is apparent that 'amuch more effective mode of operating and discharging a sodium cell was highly desirable. In particular it was desirable that the intermediate storage operation in the receiver drum be eliminated although its function was considered essential.

Anobject of the present invention hence is to provide an improved method and apparatus for the receipt of and delivery of sodium from a sodium cell, and for facilitating the delivery thereof to subsequent filtration or sedimentation operations or other purification steps. Another object is to provide a method of operation of a sodium cell, and particularly an improved delivery and discharging technique, which entirely eliminates any intermediate storage treatment of the cell product. A' further object is to provide an improved delivery and transfer technique characterized by much less exposure to contaminating atmospheres or vapors than heretofore possible. A further object is to provide new and novel apparatus for accomplishing the improved delivery operation. Other objects will appear below.

In general terms, the invention includes transfer of the sodium product directly through a transfer conduit to a transport vessel from the riser pipe with no intermediate storage. This is continued until the transport vessel is substantially fully charged, and then the said transfer is interrupted for aninterval and the cell production is accumulated in the cell collector trough for a limited but appreciable period. The accumulation approaches but does not exceed the capacity of the cell collector trough. The accumulation period is followed by reinstatement of the dircet transfer to the transport vessel. During the cumulation period cited above, the transport vessel is removed and emptied to subsequen sedimentation and filtering apparatus.

In the most preferred forms of the invention a reheating operation accompanies the direct transfer of the sodium to the transport vessel, the reheating being generally of the order of magnitude of from 25 to F. above the temperature at which the sodium is made available by the riser pipe. Also, in the most preferred forms of the invention, a small but positive flow of inert gas is passed concurrently with the sodium product through the transfer conduit, and during the periodic cumulation intervals, a positive pressure of inert gas is maintained on the top of the column of sodium in the riser pipe.

The details of the operation of the invention and of the working examples hereinafter given will be readily understood from the description hereafter and from the figures which include Figure l, a cross-sectional elevation of a sodium cell and in conjunction therewith, a preferred apparatus of the present invention, and Figure 2 which is a detailed, partially sectioned view of a quick coupling means forminga part of preferred apparatus for the invention.

Turning to Figure 1, a cell and supplemental equipment arranged for the process of the present invention -iszshown. ilfihearnajor components of thecelldncludem acell SlI1l-.2fl,ljI1ithB form ioftailargetankor'vessel, the walls and bottom thereof being composed of :a refractory material with :a .steel external shell. A bottom mounted anode 21 ?-is centrally positioned in the cell, and electrical connection is madeby appropriate means to .the bottom through a bus bar .26. Surrounding amajor portion of :the anode is:a.cylindrical cathode 22, h-aving cathodearms :or lug arms projecting from thesides thereof and -'through the walls :of the cell. The cathode :iselectrically insulated from the cell shell.27 :by means :of appropriate insulating refractory 24 packedaround the cathode arms 23. The :c'athode arms make external connection to bus bars 25 25. :to complete the electrical circuit and an annular electrolysis .zone 32 is .thus formed by the anode-cathode configuration.

Positioned above the :anode 21 and the cathode 22 is a metal assembly including in chlorine dome 29 and a collector 11. The collector 11 is an inverted channel corresponding generally in plan configuration to the annular -'electrolysis. space.32. The chlorine 'dome '29 corresponds :in general fplan configuration to the anode 2-1. .A diaphragm 33 is suspended from the chlorine tdome andcollectorassemhlyand aids in directing upward flow of sodium metal and chlorine gas as these products arereleased at the cathode :and anode respectively. 7

Connecting to't the collector channel '11is a riser pipe 121 which .extends'vertically :an. appreciable distance above the top'devel .34 .of dire cell bath. for most of this pro- ,jectingidistance, theriser pipe is fitted with extended external .fins 20 which aid in heat dissipation to the atmosphere. 'In most cases, theriseripipe is fitted with 'a :ticklermechanism :17, this being a device for dislodging calcium particles which precipitate on the walls of the of the :riser pipe. The riser'pipe maybe a'uniformcross sectionconduit, .Ibllt i-npreferred apparatus for theinven :tion, an enlarged section .12 comprises "the top terminus of the conduit. Connecting to the riser pipe near the top thereof is in transfer line 13. The transfer line .13 connects to the riser pipe periphery and provides a continuous channel from the :riserpipeto the'transport vessel. The transfer line 13 .is maintained in permanent *fixe'd alignment .by the above mentioned opening connection, and "-nsually'by means of a .brace member .18 connecting the transfer i-line 13' and the riser pipe 1 2. Nearthe bottom end ofthe transfer line 13 is a valve 14, preferably of the plug type. At theterminus of the transfer line :13 :is 'a portion 15 of a quick connecting coupling assemblyllS.

.As already mentioned in preferred apparatus for the process, an enlarged crosssection 1-2. conduit surmounts, or comprises the upper portion of the riser pipe. The transferiline 13in such installations'joins the riser pipe assembly at the horizontal shoulder 16 which-connects the enlarged section 12 to the riser pipe proper. It will be :seen that thetransfer line 13 connecting in this man ner, establishes an elliptical opening (notshown) in the shouiderof the enlarged section. The horizontal dispositionof this opening provides certain advantagesexpl'ained hereafter. .Afurther feature of the *presentenibodiment is an "extension segment 13 having a cap 30 thereon. This segment is ea pipe section closely aligned to form a projected extension of the transferline 13. The purpose of this extensionsection is to allow insertion of a closely .fitting rod, through the extension section 13 and thence through the transfer line for rod out cleaning when necessary.

Returning to the benefit of theplacement of the -con .nection :of the transfer line to theriser pipe "'12, the "prin- 'cipal advantage of 'a' connection at the shoulder '16 'of the enlarged section 12 of -the riserpipe'is that this permits continuous and effective cleaning of the entrance to the transfer .lineby portions .of .the .tickler mechanism. Hence, even though the sodium is being drawn from the coldest portion of the riser pipe, the tendency of the sodium, or impurities therein, to solidify or cake, at this point, is largely overcome.

In the most effective forms of the process, the direct transfer operation is accompanied by a reheating operation. The 'sodium'is heated from .25 to 75" -F. abovethe temperature at which the sodium is delivered at the top of the riser pipe, which is usually about 225 to -250 F. The reason for the efficacy of the heating is not fully understood, inasmuch as it would be expected that merely maintaining the 'temperatureconstant "would assure efiective and continuous flow. The heating can be accomplished by any effective means, for example, by electric strip heaters adjacent the transfer line 13, or by induction heating.

The :most preferred embodiments :of the process also include the ,step "of passing :abdry .inert gas through the 'upper part :of the riser zpipe, through the transfer line and into the transport container 28. Ordinarily, .clry

nitrogen is themost-economicalinert gas, :and may bein-' troduced by an opening or nozzle (not shown) into the top of "the riser .pipe. Alternatively, 'thecap 30 on the extension .13 can be :a nozzle for a supply-of nitrogen. 'fEhe'nitrogenris suppl-ied'to the process at a uniform pres- -sure..from .a general manifold or supply line not shown. .During the periodic eumulation "periods of the process, apositiver-pressure .ofsthetgas is maintainedat the-top of the 1rliserpipe, .but owing to the closure of the transfer line, 'thereJis substantially :no flow of gas. In'lall portions ofthe process the factual how of the inert gas is made :possiblebyismall'leaks inthe apparatus. Thus, although the quick converting coupling provides generally a satisfactoryconnection, it is not necessarily absolutely gas tight. Some leakage also occurs at the opening-or gland at the top of the riser pipe through the tickler'mecham'sm operators.

.The sodium cell is supported in an opening in the door 19 (of .the shop by support means no't s'hown. Positioned adjacent the cell during the largest segment of operation of the present invention is the transport 'vesse'l 2-8.. The transport vessel .28 is, generally, a cylindrical @steel dmrn, provided with heating elements for electrical heating if desired, and usually having appropriate external insulation material. .At the top of the transport vessel is "a nozzle 4'1'permanently welded to the transport vessel top :and "providing an opening thereto. Thenozzle 41 is provided with a half section 15 of the quick connecting coupling, this "being .in correct alignment for matching engagement with .the segment 15 of the quick connecting coupling attached to the transfer line 13. .In operation, then, the transport vessel is put :in the position indicated with the termini of the 'no'zzle'41 and the transfer line 13 in abutting position and connection is made by thecouplingelements 15 15 During a large portion-say percent-,of a eel-1 s operation, the flow of-sodium from 111611 861 pipe is allowed to continue without interruption until the vessel has been substantiallyfilled. Normally, :prior to charging the transport vessel 28, it is purged elsewhere by .a stream of dry, inertgas such' as nitrogen or helium. When the transport vessel .28 has been filled, the plug valve -14 isclosed and the coupling elements 15 .15 are disconnected and the transport vessel is removed for-discharging to subsequent sedimentation and filtering operations,., for discharge of the sodium thereto. During the absence of the transport vessel, of course electrolysis continues and the quantity of sodiunrzremaining within the cell increases. .The production during this period is cumulatedin the .riser ,pipe and in the collector channel 11. Normally, the transport vessel is necessarily away from the indicated station for a period ofifrom .15 minutes to -2' hours, and during this period the-collector channel ILpIusithe avail-able i'heightfin the riserpipe suthcient to accommodate full production of sodium in that period.

As already mentioned a particular feature of preferred apparatus of the present invention is a rapid-operating coupling mechanism, which is illustrated in some detail by Figure 2. Referring to Figure 2, the main portions of the coupling-mechanism include a sleeve 41, a movable member 44 having a spherically shaped segmental seat 45 at the upper extremity thereof. The movable member 44 is generally a short cylindrical conduit adapted to slide snugly within the sleeve member 41. The sleeve member 41 has cut into its wall a cam or slot 42. A pin 46 is affixed to the movable member 44 and has a threaded portion for mounting and engagement of a nut 47. It is seen that rotative movement of the member 44 will result in vertical movement thereof. Upon attainment of any desired vertical positioning, retention thereof is attained by fastening the nut 47 to clamp the movable member 44 in place.

Ending the transfer conduit 13 is a short and usually vertical-1y disposed segment 51, this segment having at its lower end a spherical face 52 corresponding in proportions to the spherical seat 45 of the movable member 44. In usual operation, the transport vessel 28 is positioned in the appropriate location adjacent a cell, and the movable member 44 is rotated to cause its upward movement and snug engagement with the spherical face 52 of the terminus of the transfer line '13.

It will be readily seen that this structure provides rapid engaging means for connecting the transport vessel to the delivery means of a cell installation. The use of spherical mating surfaces 45, 52 provides for close, contact and compensation for normal variations in alignment of the transfer line 13, irregularities in the floor of the building structure, etc.

Example To demonstrate the benefits of the method of the present invention, a series of cell installations, including the transport and transfer apparatus described above and shown in Figures 1 and 2 were operated for an extended period. During the operation the sodium was heated from about 240 F., the discharge temperature from the riser pipe 13, to about 290 F. or a raise of about 50 F. It was found that a reduction in the number of rodout operations of the order of 65 to 85 percent was accomplished. In addition to this drastic reduction in rodou attention, the process completely eliminated the need for hourly agitation during an intermediate storage step as heretofore required. The benefits of the process and apparatus therefor are thus clear and important.

It is apparent from the foregoing description and example that the benefits of the present improvement can be obtained using a variety of types of specific apparatus. Generally, it is of course necessary that flow through the transfer line of the apparatus be re-initiated before the accumulation of sodium in the cell is so great that the capacity of the collector channel is exceeded. When the capacity is exceeded, liquid sodium will spill over the edge and will either recombine with chlorine or will float to the external surface of the cell bath and burn by contact with atmospheric oxygen.

The proportions of the transfer line of the apparatus used are not highly critical, but the size and the position of the transfer line is, nevertheless, important. It is found that a transfer line of only moderate size is highly desirable. Thus, the transfer line conveniently has a cross-sectional area of about one percent of the riser pipe. This is, indeed, greater than the cross-sectional area required for production capacity, but the oversize assures space for a sturdy rod for clean-out purposes.

The inclination of the transfer line with respect to the horizontal is also of some significance. Generally, the transfer lines should be positioned at an angle of at least 45 to the horizontal to assure sufficiently rapid movement of the sodium through this conduit.

Icla'im: '1. In combination, a sodium cell having an inverted sodium collection trough for receiving sodium by upward displacement from an electrolysis zone, a riser pipe connecting therewith for upward flow of said sodium to a point above the cell, a transfer conduit connecting to the upper portion of said riser pipe and inclined downwardly at an angle of at least about 45 to the horizontal, heating means associated with said transfer conduit, a valve means in said conduit, and coupling means at the lower terminus of said conduit, said conduit having a transverse area of not over about one percent of the transeverse area of the riser pipe, said coupling means being adapted to couple with coupling means on a movable transport vessel for receiving sodium.

2. 'In combination, a sodium cell having an inverted sodium collection trough for receiving sodium by upward displacement from an electrolysis zone, a riser pipe connecting therewith for upward flow of said sodium to a point above the cell, said riser pipe including an upper segment of enlarged cross section connecting to the lower portion of saidriser pipe by a horizontal shoulder, a transfer conduit connecting to the riser pipe, said connection being at said shoulder, and inclined downwardly at an angle of at least about 45 to the horizontal, heating means associated with said transfer conduit, a valve means in, said c-onduit, and coupling means at the lower terminus of said conduit, said conduit having a transverse area of not over about one percent of the transverse area of the riser pipe, said 0011- pling means being adapted to couple with coupling means on a. movable transport vessel for receiving sodium, and an extension conduit connecting to the enlarged portion of the riser pipe and being aligned with the transfer conduit, and closure means for said extension conduit, whereby an aligning channel is provided for insertion of a clean-out means for the transfer conduit.

3. In the manufacture of sodium metal by the electrolysis of a fused electrolyte bath having a greater density than the liquid sodium, and under conditions wherein the sodium is discharged from the electrolysis zone accompanied by coformed metallic impurities, said sodium being discharged from the electrolysis zone by the upward displacement by the electrolyte, collection in an inverted trough and upward flow therefrom through a riser pipe wherein the sodium is cooled to a temperature of about 225 to 250 F. and the co-deposited metal impurity is precipitated in part and settled to the cell interior, the improved discharge procedure comprising immediately passing the resultant partly purified sodium metal directly from the upper end of the riser pipe to a transport vessel, said passing being at a higher velocity relative to the upward velocity in the riser pipe and being accompanied by heating of the sodium from about 25 to 75 F. above the discharge temperature from the riser pipe, discontinuing said direct flow to the transport vessel at periodic intervals for disengaging temporarily the transport vessel and accumulating the sodium metal produced in the inverted trough until the transfer vessel is reengaged.

4. In the manufacture of sodium metal by the electrolysis of a fused electrolyte bath having a greater density than the liquid sodium, and under conditions wherein the sodium is discharged from the electrolysis zone accompanied by co-formed calcium metallic irnpurities, said sodium being discharged from the electrolysis zone by the upward displacement by the electrolyte, collection in an inverted trough and upward flow therefrom through a riser pipe wherein the sodium is cooled to a temperature of about 225 to 250 F., and the calcium impurity is precipitated in part and settled to the cell interior, the improved discharge procedure comprising immediately passing the resultant partly purifled sodium metal directly from the upper end of the riser pipe to a transport vessel, said passing being at a higher velocity .relative to the upward velocity in the ,riser pipe and being accompanied by heating of .the .50.- -d'i-um from about 25 .to -75? F. above ithefl said temperat-ure .irom the riser pipe, discontinuing said ldirect flow to the transport vessel at :periodiedntervals vfor disengaging temporarily ithe transport vessel-and accumulating thesodium metal produced in the inverted trough until theti'ans'fer vessel is reengaged.

References Cited in thefi-le of this patent .5 I UNITED STATES PATENTS .rl,839;756 :Grebeet 'al, Jams, 1932 Hulse .Sept. 2.0, 1938 

1. IN COMBINATION, A SODIUM CELL HAVING AN INVERTED SODIUM COLLECTION TROUGH FOR RECEIVING SODIUM BY UPWARD DISPLACEMENT FROM AN ELECTROLYSIS ZONE, A RISER PIPE CONNECTING THEREWITH FOR UPWARD FLOW OF SAID SODIUM TO A POINT ABOVE THE CELL, A TRANSFER CONDUIT CON NECTING TO THE UPPER PORTION OF SAID RISER PIPE AND INCLINED DOWNWARDLY AT AN ANGLE OF AT LEAST ABOUT 45* TO THE HORIZONTAL, HEATING MEANS ASSOCIATED WITH SAID TRANSFER CONDUIT, A VALVE MEANS IN SAID CONDUIT, AND COUPLING MEANS AT THE LOWER TERMINUS OF SAID CONDUIT, SAID CONDUIT HAVING A TRANSVERSE AREA OF NOT OVER ABOUT ONE PERCENT OF THE TRANSEVERSE AREA OF THE RISER PIPE, SAID COUPLING MEANS BEING ADAPTED TO COUPLE WITH COUPLING MEANS ON A MOVABLE TRANSPORT VESSEL FOR RECEIVING SODIUM. 